Pen push button



FIG. 1 is a front side bottom perspective view of a pen push button showing my new design;

FIG. 2 is a front elevational view thereof which is a mirror image of the back side, right side and left side thereof;

FIG. 3 is a top plan view thereof; and,

FIG. 4 is a bottom plan view thereof.

The broken lines showing the pen body and a portion of the bottom view are included for the purpose of illustrating environmental structure and form no part of the claimed design. 

The ornamental design for a pen push button, as shown and described. 